cnp3-ebook/protocols/ipv6 — English @ Weblate

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149 ../../protocols/ipv6.rst:499

	English Header compression on low bandwidth links 41/10000 · 41
150 ../../protocols/ipv6.rst:501

	English Given the size of the IPv6 header, it can cause huge overhead on low bandwidth links, especially when small packets are exchanged such as for Voice over IP applications. In such environments, several techniques can be used to reduce the overhead. A first solution is to use data compression in the datalink layer to compress all the information exchanged [Thomborson1992]_. These techniques are similar to the data compression algorithms used in tools such as :manpage:`compress(1)` or :manpage:`gzip(1)` :rfc:`1951`. They compress streams of bits without taking advantage of the fact that these streams contain IP packets with a known structure. A second solution is to compress the IP and TCP header. These header compression techniques, such as the one defined in :rfc:`5795` take advantage of the redundancy found in successive packets from the same flow to significantly reduce the size of the protocol headers. Another solution is to define a compressed encoding of the IPv6 header that matches the capabilities of the underlying datalink layer :rfc:`4944`. 1063/10000 · 1063
151 ../../protocols/ipv6.rst:503

	English The last type of `IPv6 header extension` is the `Routing` header. The ``type 0`` routing header defined in :rfc:`2460` is an example of an IPv6 option that must be processed by some routers. This option is encoded as shown below. 229/10000 · 229
152 ../../protocols/ipv6.rst:509

	English The Type 0 routing header (:rfc:`2460`) 39/10000 · 39
153 ../../protocols/ipv6.rst:512

	English The type 0 routing option was intended to allow a host to indicate a loose source route that should be followed by a packet by specifying the addresses of some of the routers that must forward this packet. Unfortunately, further work with this routing header, including an entertaining demonstration with scapy_ [BE2007]_ , revealed severe security problems with this routing header. For this reason, loose source routing with the type 0 routing header has been removed from the IPv6 specification :rfc:`5095`. 510/10000 · 510
154 ../../protocols/ipv6.rst:520

	English ICMP version 6 14/10000 · 14
155 ../../protocols/ipv6.rst:522

	English It is sometimes necessary for intermediate routers or the destination host to inform the sender of the packet of a problem that occurred while processing a packet. In the TCP/IP protocol suite, this reporting is done by the Internet Control Message Protocol (ICMP). ICMPv6 is defined in :rfc:`4443`. It is used both to report problems that occurred while processing an IPv6 packet, but also to distribute addresses. 415/10000 · 415
156 ../../protocols/ipv6.rst:524

	English ICMPv6 messages are carried inside IPv6 packets (the `Next Header` field for ICMPv6 is ``58``). Each ICMP message contains a 32 bits header with an 8 bits `type` field, a `code` field and a 16 bits checksum computed over the entire ICMPv6 message. The message body contains a copy of the IPv6 packet in error. 309/10000 · 309
157 ../../protocols/ipv6.rst:530

	English ICMP version 6 packet format 28/10000 · 28
158 ../../protocols/ipv6.rst:533

	English ICMPv6 specifies two classes of messages : error messages that indicate a problem in handling a packet and informational messages. Four types of error messages are defined in :rfc:`4443` : 188/10000 · 188
159 ../../protocols/ipv6.rst:539

	English ``1`` : `Destination Unreachable`. Such an ICMPv6 message is sent when the destination address of a packet is unreachable. The `code` field of the ICMP header contains additional information about the type of unreachability. The following codes are specified in :rfc:`4443` 273/10000 · 273
160 ../../protocols/ipv6.rst:538

	English Destination Unreachable. Such an ICMPv6 message is sent when the destination address of a packet is unreachable. The code field of the ICMP header contains additional information about the type of unreachability. The following codes are specified in RFC 4443 258/10000 · 258
161 ../../protocols/ipv6.rst:536

	English ``0`` : No route to destination. This indicates that the router that sent the ICMPv6 message did not have a route towards the packet's destination 146/10000 · 146
162 ../../protocols/ipv6.rst:537

	English ``1`` : Communication with destination administratively prohibited. This indicates that a firewall has refused to forward the packet towards its final destination. 163/10000 · 163
163 ../../protocols/ipv6.rst:538

	English ``2`` : Beyond scope of source address. This message can be sent if the source is using link-local addresses to reach a global unicast address outside its subnet. 162/10000 · 162
164 ../../protocols/ipv6.rst:539

	English ``3`` : Address unreachable. This message indicates that the packet reached the subnet of the destination, but the host that owns this destination address cannot be reached. 173/10000 · 173
165 ../../protocols/ipv6.rst:540

	English ``4`` : Port unreachable. This message indicates that the IPv6 packet was received by the destination, but there was no application listening to the specified port. 164/10000 · 164
166 ../../protocols/ipv6.rst:541

	English ``2`` : Packet Too Big. The router that was to send the ICMPv6 message received an IPv6 packet that is larger than the MTU of the outgoing link. The ICMPv6 message contains the MTU of this link in bytes. This allows the sending host to implement Path MTU discovery :rfc:`1981` 276/10000 · 276
167 ../../protocols/ipv6.rst:542

	English ``3`` : Time Exceeded. This error message can be sent either by a router or by a host. A router would set `code` to `0` to report the reception of a packet whose `Hop Limit` reached `0`. A host would set `code` to `1` to report that it was unable to reassemble received IPv6 fragments. 285/10000 · 285
168 ../../protocols/ipv6.rst:543

	English ``4`` : Parameter Problem. This ICMPv6 message is used to report either the reception of an IPv6 packet with an erroneous header field (code `0`) or an unknown `Next Header` or IP option (codes `1` and `2`). In this case, the message body contains the erroneous IPv6 packet and the first 32 bits of the message body contain a pointer to the error. 347/10000 · 347

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